At the time of writing, shares in the company fell nearly 16% on the news that paper production and sales in 2010/11 would be "materially lower" than originally planned following the factory glitch, according to the group.
In a statement, the group, which supplies banknotes to banks, including the Bank of England, said it had become apparent that "some paper production has failed to meet certain quality specifications".
It added: "The full impact on the current year's financial results and on the group's prospects has yet to be determined.
"A further announcement will be made as soon as the board has been able to assess the financial and operational implications of these matters."
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